Silicon carbide focus ring for plasma etching system

ABSTRACT

A high resistivity silicon carbide focus ring for use in a plasma etching system is described. The focus ring comprises an upper surface, a lower surface, an inner radial edge, and an outer radial edge, and is configured to surround a substrate on a substrate holder in a plasma processing system. The focus ring comprises high resistivity silicon carbide having a resistivity greater than or equal to about 100 ohm-cm.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a focus ring for use in a plasma processingsystem and, more particularly, to a high resistivity silicon carbidefocus ring for use in a plasma etching system.

2. Description of Related Art

The fabrication of integrated circuits (IC) in the semiconductorindustry typically employs plasma to create and assist surface chemistrywithin a vacuum processing system necessary to remove material from anddeposit material to a substrate. In general, plasma is formed within theprocessing system under vacuum conditions by heating electrons toenergies sufficient to sustain ionizing collisions with a suppliedprocess gas. Moreover, the heated electrons can have energy sufficientto sustain dissociative collisions and, therefore, a specific set ofgases under predetermined conditions (e.g., chamber pressure, gas flowrate, etc.) are chosen to produce a population of charged species andchemically reactive species suitable to the particular process beingperformed within the system (e.g., etching processes where materials areremoved from the substrate or deposition processes where materials areadded to the substrate).

Although the formation of a population of charged species (ions, etc.)and chemically reactive species is necessary for performing the functionof the plasma processing system (i.e. material etch, materialdeposition, etc.) at the substrate surface, other component surfaces onthe interior of the processing chamber are exposed to the physically andchemically active plasma and, in time, can erode. The erosion of exposedcomponents in the processing system can lead to a gradual degradation ofthe plasma processing performance and ultimately to complete failure ofthe system. Therefore, in order to minimize the damage sustained byexposure to the processing plasma, a consumable or replaceablecomponent, such as one fabricated from silicon, quartz, alumina, carbon,or silicon carbide, can be inserted within the processing chamber toprotect the surfaces of more valuable components that would imposegreater costs during frequent replacement and/or to affect changes inthe process. Furthermore, it is desirable to select surface materialsthat minimize the introduction of unwanted contaminants, impurities,etc. to the processing plasma and possibly to the devices formed on thesubstrate. Often times, these consumables or replaceable components areconsidered part of the process kit, which is frequently maintainedduring system cleaning.

SUMMARY OF THE INVENTION

The invention relates to a focus ring for use in a plasma processingsystem and, more particularly, to a high resistivity silicon carbidefocus ring for use in a plasma etching system.

According to one embodiment, a high resistivity silicon carbide focusring for use in a plasma etching system is described. The focus ringcomprises an upper surface, a lower surface, an inner radial edge, andan outer radial edge, and is configured to surround a substrate on asubstrate holder in a plasma processing system. The focus ring compriseshigh resistivity silicon carbide having a resistivity greater than orequal to about 100 ohm-cm.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 provides a schematic illustration of a plasma processing systemaccording to an embodiment;

FIG. 2A shows a top view of a focus ring according to an embodiment;

FIG. 2B shows a cross-sectional view of the focus ring depicted in FIG.2A;

FIG. 3A presents exemplary data for processing a substrate;

FIG. 3B presents additional exemplary data for processing a substrate;and

FIG. 4 illustrates a method of processing a substrate according to anembodiment.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

A focus ring for use in a plasma processing system is disclosed invarious embodiments. However, one skilled in the relevant art willrecognize that the various embodiments may be practiced without one ormore of the specific details, or with other replacement and/oradditional methods, materials, or components. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of various embodiments ofthe invention. Similarly, for purposes of explanation, specific numbers,materials, and configurations are set forth in order to provide athorough understanding of the invention. Nevertheless, the invention maybe practiced without specific details. Furthermore, it is understoodthat the various embodiments shown in the figures are illustrativerepresentations and are not necessarily drawn to scale.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention, but do not denote that theyare present in every embodiment. Thus, the appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily referring to the same embodimentof the invention. Furthermore, the particular features, structures,materials, or characteristics may be combined in any suitable manner inone or more embodiments. Various additional layers and/or structures maybe included and/or described features may be omitted in otherembodiments.

In material processing methodologies, pattern etching comprises theapplication of a thin layer of radiation sensitive material, such asphotoresist, to an upper surface of a substrate, that is subsequentlypatterned in order to provide a mask for transferring this featurepattern to the underlying thin film during etching. The patterning ofthe radiation-sensitive material generally involves exposure of thelithographic layer to a geometric pattern of electromagnetic (EM)radiation using, for example, a micro-lithography system, followed bythe removal of the irradiated regions of the radiation-sensitivematerial (as in the case of positive photoresist), or non-irradiatedregions (as in the case of negative photoresist) using a developingsolvent.

In plasma processing, a focus ring can, for example, be configured tosurround a substrate on a substrate holder, and be employed to adjustand/or control the properties of the process chemistry local to theperipheral edge of the substrate. For conventional plasma processingsystems, the focus ring comprises a ring of silicon, for instance foroxide etching, that rests atop the substrate holder and surrounds thesubstrate periphery. For other conventional plasma processing systems,the focus ring comprises a ring of quartz, for instance for siliconetching, that rests atop the substrate holder and surrounds thesubstrate periphery. However, the inventors have observed that focusrings prepared from conventional materials have caused non-uniformplasma processing of the substrate. For example, the critical dimension(CD) bias has been observed to vary across the substrate, which may beunacceptable due to loss in device yield.

Therefore, according to an embodiment, a high resistivity siliconcarbide focus ring for use in a plasma etching system is described. Thefocus ring comprises an upper surface, a lower surface, an inner radialedge, and an outer radial edge, and is configured to surround asubstrate on a substrate holder in a plasma processing system. The focusring comprises high resistivity silicon carbide having a resistivitygreater than or equal to about 100 ohm-cm.

According to an embodiment, a plasma processing system 1 is depicted inFIG. 1 comprising a plasma processing chamber 10, an upper assembly 20,an electrode plate assembly 24, a substrate holder 30 for supporting asubstrate 35, and a pumping duct 40 coupled to a vacuum pump (not shown)for providing a reduced pressure atmosphere 11 in plasma processingchamber 10. Plasma processing chamber 10 can facilitate the formation ofa processing plasma in process space 12 adjacent substrate 35. Theplasma processing system 1 can be configured to process substrates ofany size, such as 200 mm substrates, 300 mm substrates, or larger. Forexample, the plasma processing system 1 may comprise a plasma etchingsystem.

In the illustrated embodiment, electrode plate assembly 24 comprises anelectrode plate 26 (FIG. 1) and an electrode 28 (FIG. 1). In analternate embodiment, upper assembly 20 can comprise at least one of acover, a gas injection assembly, and an upper electrode impedance matchnetwork. The electrode plate assembly 24 can be coupled to a source ofradio frequency (RF) energy, such as an RF generator. In anotheralternate embodiment, the upper assembly 20 comprises a cover coupled tothe electrode plate assembly 24, wherein the electrode plate assembly 24is maintained at an electrical potential equivalent to that of theplasma processing chamber 10. For example, the plasma processing chamber10, the upper assembly 20, and the electrode plate assembly 24 can beelectrically connected to ground potential.

Plasma processing chamber 10 may further comprise an optical viewport 16coupled to a deposition shield 14. Optical viewport 16 may comprise anoptical window 17 coupled to the backside of an optical windowdeposition shield 18, and an optical window flange 19 may be configuredto couple optical window 17 to the optical window deposition shield 18.Sealing members, such as O-rings, can be provided between the opticalwindow flange 19 and the optical window 17, between the optical window17 and the optical window deposition shield 18, and between the opticalwindow deposition shield 18 and the plasma processing chamber 10.Optical viewport 16 can permit monitoring of optical emission from theprocessing plasma in process space 12.

Substrate holder 30 may further comprise a vertical translational device50 surrounded by a bellows 52 coupled to the substrate holder 30 and theplasma processing chamber 10, and configured to seal the verticaltranslational device 50 from the reduced pressure atmosphere 11 inplasma processing chamber 10. Additionally, a bellows shield 54 may becoupled to the substrate holder 30 and configured to protect the bellows52 from the processing plasma. Substrate holder 30 further comprises afocus ring 60, and may optionally comprise a shield ring 62.Furthermore, a baffle plate 64 can extend about a periphery of thesubstrate holder 30. The focus ring 60 comprises high resistivitysilicon carbide having a resistivity greater than or equal to about 100ohm-cm.

Substrate 35 can be transferred into and out of plasma processingchamber 10 through a slot valve (not shown) and chamber feed-through(not shown) via robotic substrate transfer system where it is receivedby substrate lift pins (not shown) housed within substrate holder 30 andmechanically translated by devices housed therein. Once substrate 35 isreceived from substrate transfer system, it is lowered to an uppersurface of substrate holder 30.

Substrate 35 may be affixed to the substrate holder 30 via a mechanicalclamping system or an electrical clamping system, such as anelectrostatic clamping system. Furthermore, substrate holder 30 mayfurther include a cooling system including a re-circulating coolant flowthat receives heat from substrate holder 30 and transfers heat to a heatexchanger system (not shown), or when heating, transfers heat from theheat exchanger system. Moreover, gas may be delivered to the back-sideof substrate 35 via a backside gas system (not shown) to improve thegas-gap thermal conductance between substrate 35 and substrate holder30. Such a system may be utilized when temperature control of thesubstrate is required at elevated or reduced temperatures. In otherembodiments, heating elements, such as resistive heating elements, orthermoelectric heaters/coolers may be included.

In the illustrated embodiment shown in FIG. 1, substrate holder 30 maycomprise an electrode through which RF power is coupled to theprocessing plasma in process space 12. For example, substrate holder 30can be electrically biased at a RF voltage via the transmission of RFpower from a RF generator (not shown) through an impedance match network(not shown) to substrate holder 30. The RF bias may serve to heatelectrons to form and maintain plasma. In this configuration, the systemcan operate as a reactive ion etch (RIE) reactor, wherein the chamberand upper gas injection electrode serve as ground surfaces. A typicalfrequency for the RF bias can range from about 1 MHz to about 100 MHz,for example, about 13.56 MHz. RF systems for plasma processing are wellknown to those skilled in the art.

Alternately, the processing plasma in process space 12 can be formedusing a parallel-plate, capacitively coupled plasma (CCP) source, aninductively coupled plasma (ICP) source, any combination thereof, andwith and without magnet systems. Alternately, the processing plasma inprocess space 12 can be formed using electron cyclotron resonance (ECR).In yet another embodiment, the processing plasma in process space 12 isformed from the launching of a Helicon wave. In yet another embodiment,the processing plasma in process space 12 is formed from a propagatingsurface wave.

Referring now to an illustrated embodiment depicted in FIG. 2A (top planview) and FIG. 2B (cross sectional view), a focus ring 600 is described.The focus ring 600 can form a ring comprising an upper surface 603, alower surface 604, an inner radial edge 601, and an outer radial edge602.

The focus ring 600 comprises high resistivity silicon carbide having aresistivity greater than or equal to about 100 ohm-cm. Additionally, theresistivity of the silicon carbide may be greater than or equal to 1000ohm-cm. Additionally yet, the resistivity of the silicon carbide mayrange from about 100 ohm-cm to about 10⁶ ohm-cm.

The focus ring 600 comprises high resistivity silicon carbide having aresistivity greater than or equal to about 100 ohm-cm at a temperatureranging from about 50 degrees C. to about 200 degrees C. For example,the temperature may be about 150 degrees C. Additionally, theresistivity of the silicon carbide may be greater than or equal to 1000ohm-cm at a temperature ranging from about 50 degrees C. to about 200degrees C. (for example, the temperature may be about 150 degrees C.).Additionally, yet, the resistivity of the silicon carbide may range fromabout 100 ohm-cm to about 10⁶ ohm-cm at a temperature ranging from about50 degrees C. to about 200 degrees C. (for example, the temperature maybe about 150 degrees C.). Low resistivity silicon carbide may beconsidered to comprise a resistivity of less than about 10 ohm-cm at atemperature of about 150 degrees C.

Focus ring 600 may comprise high resistivity silicon carbide.Alternatively, focus ring 600 may consist essentially of highresistivity silicon carbide. Alternatively yet, focus ring 600 mayconsist of high resistivity silicon carbide.

Focus ring 600 may comprise vapor deposited high resistivity siliconcarbide. For example, focus ring 600 may comprise chemical vapordeposited high resistivity silicon carbide. Alternatively, focus ring600 may comprise sintered high resistivity silicon carbide. Themanufacture of focus ring 600 may further comprise machining, milling,planarizing, grinding, polishing, coating, laser cutting, water-jetcutting, etc.

Focus ring 600 may comprise a plurality of layers, wherein at least oneof the plurality of layers comprises high resistivity silicon carbide.Additionally, focus ring 600 may comprise a coating applied to at leastone of the upper surface 603, the lower surface 604, the inner radialedge 601, and the outer radial edge 602. The coating may comprise asilicon-containing coating or a ceramic coating. For example, thecoating may comprise a vapor deposited coating or a spray coating.Additionally, for example, the coating may include at least one of aIII-column element and a Lanthanon element, for example. The coating maycomprise at least one of Al₂O₃, Yttria (Y₂O₃), Sc₂O₃, Sc₂F₃, YF₃, La₂O₃,CeO₂, Eu₂O₃, and DyO₃. Methods of applying spray coatings are well knownto those skilled in the art of surface material treatment.

The focus ring 600 can have a thickness ranging from about 0.5 to about10 mm. Alternatively, the thickness can range from about 1 to about 5mm, or the thickness can be approximately 1 mm.

Focus ring 600 may comprise a centering feature configured to center thefocus ring 600 on the substrate holder. For example, the centeringfeature may comprise a flat or a notch formed in the outer radial edge602 that is configured to mate with a similar feature formed in thesubstrate holder. Furthermore, as illustrated in FIG. 2B, focus ring 600may comprise a step 610 formed in the inner radial edge 601, andconfigured to mate in close proximity with substrate 625.

Focus ring 600 may further comprise one or more wear indicators coupledto at least one of the upper surface 603 or the lower surface 604. Forexample, the one or more wear indicators may comprise a blind holeformed in the upper surface 603 and extending to a depth from the uppersurface 603. The depth may comprise a fraction of the distance betweenthe upper surface 603 and the lower surface 604. Additionally, forexample, the one or more wear indicators may comprise a blind holeformed in the lower surface 604 and extending to a depth from the lowersurface 604. The depth may comprise a fraction of the distance betweenthe upper surface 603 and the lower surface 604. Each wear indicator mayhave a constant length and width. Alternatively, each wear indicator mayhave a different length, and/or different width. Alternatively yet, eachwear indicator may comprise a variable width along its length. As thefocus ring 600 erodes, the size of the blind hole varies.

Visual inspection may be utilized to determine the extent of erosion forfocus ring 600. For example, this observation can be made fromrun-to-run, while monitoring the focus ring 600 through an opticalwindow, such as the optical window 17 in FIG. 1.

Additionally, each wear indicator may be placed at different radiallocations on the focus ring 600 in order to observe radial variations inthe consumption of the focus ring 600. Alternatively, each wearindicator may be placed at different azimuthal locations on the focusring 600 in order to observe azimuthal variations in the consumption ofthe focus ring 600. A wear indicator may have a length ranging fromabout 1 mm to about 5 mm. Alternatively, the length may range from about0.25 mm to about 1 mm, or the length may be approximately 0.5 mm.Alternately, a wear indicator may be a fraction of the thickness offocus ring 600 within a fractional range from about 10% to about 90%.Alternatively, the fraction of the focus ring thickness can have afractional range from about 25 to about 75%, or the fraction of thefocus ring thickness can be approximately 50%. The one or more wearindicators may, for example, be fabricated using at least one ofmachining, etching, laser-milling, and sonic-milling.

Referring now to FIG. 4, an exemplary method for performing a patterntransfer process is presented. The method includes a flow chart 500beginning in 510 with forming a film stack on a substrate. The filmstack may comprise a polysilicon layer, a hard mask layer formed on thepolysilicon (polycrystalline silicon) layer, an anti-reflective coating(ARC) layer formed on the hard mask layer, and a radiation sensitivelayer formed on the ARC layer. For example, the film stack mayfacilitate the formation of a gate stack.

In 520, a pattern is formed in the radiation sensitive mask layer usinga lithographic process. The radiation sensitive mask layer may include aresist. For example, the resist may comprise 248 nm (nanometer) resists,193 nm resists, 157 nm resists, EUV (extreme ultraviolet) resists, orelectron sensitive resists. The radiation sensitive layer may be formedusing a track system. For example, the track system can comprise a CleanTrack ACT 8, ACT 12, or Lithius resist coating and developing systemcommercially available from Tokyo Electron Limited (TEL). Other systemsand methods for forming a photo-resist film on a substrate are wellknown to those skilled in the art of spin-on resist technology. Theexposure to electromagnetic (EM) radiation may be performed in a dry orwet photo-lithography system, or an electron beam lithography system.

In 530, a lateral dimension of the radiation sensitive mask layer isoptionally trimmed. The trimming process may comprise an etchingprocess, such as a dry etching process or a wet etching process. The dryetching process may include a dry plasma etching process or a drynon-plasma etching process. For example, the trimming process mayinclude trimming the pattern by introducing a process gas including asincipient ingredients a fluorocarbon gas and an oxygen-containing gas,forming plasma from the process gas, and exposing the substrate to theplasma.

In 540, the trimmed pattern is transferred to the ARC layer. The patterntransfer process may comprise a first etching process, such as a dryetching process or a wet etching process. The dry etching process mayinclude a dry plasma etching process or a dry non-plasma etchingprocess. For example, the first etching process may include transferringthe pattern by introducing a process gas including as incipientingredients a fluorocarbon gas and an oxygen-containing gas, formingplasma from the process gas, and exposing the substrate to the plasma.The first etching process for transferring the trimmed pattern to theARC layer may be performed simultaneously with trimming the pattern.Furthermore, following the transferring of the trimmed pattern to theARC layer, an over-etch process on the ARC layer may optionally beperformed.

In 550, the trimmed pattern is transferred to the hard mask layer usinga second etching process, such as a dry etching process or a wet etchingprocess. The dry etching process may include a dry plasma etchingprocess or a dry non-plasma etching process. For example, the secondetching process may include introducing a process gas including asincipient ingredients one or more fluorocarbon gases, forming plasmafrom the process gas, and exposing the substrate to the plasma.

In 560, the trimmed pattern is transferred to the polysilicon layerusing a third etching process, such as a dry etching process or a wetetching process. The dry etching process may include a dry plasmaetching process or a dry non-plasma etching process. For example, thethird etching process may comprise one or more etching steps using ahalogen-containing plasma chemistry, such as a HBr-containing plasmachemistry. The one or more etch steps may include a first main etchstep, a second main etch step, and an over-etch step.

The trimming process, the first etching process, the second etchingprocess, the third etching process, and the over-etch process(es) may beperformed in a plasma processing system. The plasma processing systemmay comprise various elements, such as described in FIG. 1.

In one embodiment, a method of performing a pattern transfer process ona substrate with reduced variability in process performance across thesubstrate is provided. For example, a process parameter space for aseries of process steps can comprise a chamber pressure of about 1 toabout 1000 mtorr (1 torr) (e.g., about 10 mtorr to about 150 mtorr), aprocess gas flow rate ranging from about 1 to about 1000 sccm, an upperelectrode RF bias ranging from about 0 to about 2000 W, and a lowerelectrode RF bias ranging from about 10 to about 2000 W. Also, the upperelectrode bias frequency can range from about 0.1 MHz to about 200 MHz,e.g., 60 MHz. In addition, the lower electrode bias frequency can rangefrom about 0.1 MHz to about 100 MHz, e.g., 2 MHz.

According to an example, a method of reducing critical dimension (CD)bias variability in a pattern transfer process is presented. The processsteps and parameters are provided in Table 1 for a quartz (QTZ) focusring (F/R) having a low resistivity silicon carbide base layer.Furthermore, the process steps and parameters are provided in Table 2for a high resistivity (H.R.) silicon carbide (SiC) F/R.

Table 1 and Table 2 provide process conditions for the pattern transferprocess, including a trim/ARC pattern transfer step (e.g., 530 and 540in FIG. 8), an ARC over-etch step, a hard mask pattern transfer step(e.g., 550 in FIG. 8), and a polysilicon pattern transfer step (e.g.,560 in FIG. 8). The polysilicon pattern transfer step includes a firstpolysilicon etch step, a second polysilicon etch step, and an overetchstep. For each step, the pressure (P, mtorr), the RF power (coupled tothe upper electrode, UEL, and the lower electrode, LEL in watts, W), theflow rate (standard cubic centimeters per minute, sccm) for each processingredient, the center (C) and edge (E) substrate backside pressures(B.P.) (torr), and the temperature setting for the UEL (T), chamber wall(W), substrate holder center (B) and edge (Edge) are provided.

TABLE 1 POWER TEMP T/W/B QUARTZ (QTZ) F/R P UEL/LEL SCCM B.P. (C/E)(Edge) PROCESS STEP (mtorr) (W) HBr O₂ CF₄ C₄F₈ CH₂F₂ He N₂ (torr) (deg.C.) TRIM/ARC PATTERN TRANSFER 12 300/0 12 48 10/50 80/60/68(53) ARCOVER-ETCH 20 300/65 2.5 70 8 10/50 80/60/68(53) HARD MASK PATTERN 15500/160 75 20 50 10/50 80/60/68(53) TRANSFER POLYSILICON ETCH STEP 1 20600/100 550 4 10/10 80/60/68(53) POLYSILICON ETCH STEP 2 10 300/30 250 460 10/10 80/60/68(53) POLYSILICON OVER-ETCH 40 135/45 500 9 440 10/1080/60/68(53) O2 FLASH 150 375/0 200 3/3 80/60/68(53)

TABLE 2 POWER TEMP T/W/B H.R. SILICON CARBIDE (SiC) F/R P UEL/LEL SCCMB.P. (C/E) (Edge) PROCESS STEP (mtorr) (W) HBr O₂ CF₄ C₄F₈ CH₂F₂ He N₂(torr) (deg. C.) TRIM/ARC PATTERN TRANSFER 12 300/0 12 48 10/5080/60/70(65) ARC OVER-ETCH 20 300/65 2.5 70 8 10/50 80/60/70(65) HARDMASK PATTERN 15 500/160 75 20 50 10/50 80/60/70(65) TRANSFER POLYSILICONETCH STEP 1 20 600/100 550 4 10/10 80/60/70(65) POLYSILICON ETCH STEP 210 300/30 250 4 60 10/10 80/60/70(65) POLYSILICON OVER-ETCH 40 135/45500 9 440 10/10 80/60/70(65) O2 FLASH 150 375/0 200 3/3 80/60/70(65)

The pattern transfer process, illustrated in Table 1 and Table 2, isconducted with a quartz F/R and a H.R. SiC F/R, respectively. The CDbias (i.e., difference between the initial CD and the final CD) isapproximately the same for both F/Rs. For example, with a quartz F/R,the CD bias is 25.6 nm (3σ=3.5 nm) for dense structures (e.g., closelyspaced structures) and the CD bias is 25.5 nm (3σ=3.2 nm) for isolatedstructures (e.g., widely spaced structures). Additionally, for example,with a H.R. SiC F/R, the CD bias is 26.9 nm (3σ=2.6 nm) for densestructures (e.g., closely spaced structures) and the CD bias is 26.4 nm(3σ=3.0 nm) for isolated structures (e.g., widely spaced structures).

However, the variation in the CD bias across the substrate is markedlydifferent for the different F/R compositions. Referring now to FIGS. 3Aand 3B, the CD bias (A, angstroms) as a function of the distance fromthe substrate center (m, millimeters) is provided for dense structuresand isolated structures, respectively. As evident in both FIGS. 3A and3B, the inventors have observed a reduction in the CD bias variationparticularly near the substrate edge. For instance, with the quartz F/R,the variation may be as great as 150 A. This variation is substantiallyreduced when utilizing a high resistivity silicon carbide F/R.Furthermore, the inventors have observed a reduction in particlegeneration with the use of the H.R. SiC F/R versus the QTZ F/R.

Although only certain embodiments of this invention have been describedin detail above, those skilled in the art will readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention.Accordingly, all such modifications are intended to be included withinthe scope of this invention.

1. A focus ring for surrounding a substrate on a substrate holder in aplasma processing system, comprising: a focus ring having an uppersurface, a lower surface, an inner radial edge, and an outer radialedge, wherein said focus ring comprises high resistivity silicon carbidehaving a resistivity greater than or equal to about 100 ohm-cm.
 2. Thefocus ring of claim 1, wherein said resistivity is greater than or equalto about 1000 ohm-cm.
 3. The focus ring of claim 1, wherein saidresistivity ranges from about 100 ohm-cm to about 10⁶ ohm-cm.
 4. Thefocus ring of claim 1, wherein said focus ring consists essentially ofhigh resistivity silicon carbide.
 5. The focus ring of claim 1, whereinsaid focus ring consists of high resistivity silicon carbide.
 6. Thefocus ring of claim 1, wherein said focus ring comprises vapor depositedhigh resistivity silicon carbide.
 7. The focus ring of claim 1, whereinsaid focus ring comprises chemical vapor deposited high resistivitysilicon carbide.
 8. The focus ring of claim 1, wherein said focus ringcomprises sintered high resistivity silicon carbide.
 9. The focus ringof claim 1, wherein said focus ring comprises a centering featureconfigured to center said focus ring on said substrate holder.
 10. Thefocus ring of claim 1, wherein said focus ring comprises one or morewear indicators coupled to at least one of said upper surface or saidlower surface.
 11. The focus ring of claim 10, wherein said one or morewear indicators comprises a hole in said upper surface and extending toa depth from said upper surface, said depth comprising a fraction of thedistance between said upper surface and said lower surface.
 12. Thefocus ring of claim 10, wherein said one or more wear indicatorscomprise a hole in said lower surface and extending to a depth from saidlower surface, said depth comprising a fraction of the distance betweensaid upper surface and said lower surface.
 13. The focus ring of claim1, wherein said focus ring comprises a plurality of layers, wherein atleast one of said plurality of layers comprises high resistivity siliconcarbide.
 14. The focus ring of claim 1, wherein said focus ringcomprises a coating applied to at least one of said upper surface, saidlower surface, said inner radial edge, and said outer radial edge. 15.The focus ring of claim 1, wherein said focus ring comprises a stepformed in said inner radial edge.